Commit 9a38a885 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
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tracing: Add a method to pass in trace_array descriptor to option files 



In preparation of having the multi buffer instances having their own trace
option flags, the trace option files needs a way to not only pass in the
flag they represent, but also the trace_array descriptor.

A new field is added to the trace_array descriptor called trace_flags_index,
which is a 32 byte character array representing a bit. This array is simply
filled with the index of the array, where

  index_array[n] = n;

Then the address of this array is passed to the file callbacks instead of
the index of the flag index. Then to retrieve both the flag index and the
trace_array descriptor:

  data is the passed in argument.

  index = *(unsigned char *)data;

  data -= index;

  /* Now data points to the address of the array in the trace_array */

  tr = container_of(data, struct trace_array, trace_flags_index);

Suggested-by: default avatarJohannes Berg <johannes.berg@intel.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 983f938a

kernel/trace/trace.c

+60 −7
Original line number Diff line number Diff line
@@ -6186,14 +6186,51 @@ static const struct file_operations trace_options_fops = { 
	.llseek	= generic_file_llseek,

};



/*

 * In order to pass in both the trace_array descriptor as well as the index

 * to the flag that the trace option file represents, the trace_array

 * has a character array of trace_flags_index[], which holds the index

 * of the bit for the flag it represents. index[0] == 0, index[1] == 1, etc.

 * The address of this character array is passed to the flag option file

 * read/write callbacks.

 *

 * In order to extract both the index and the trace_array descriptor,

 * get_tr_index() uses the following algorithm.

 *

 *   idx = *ptr;

 *

 * As the pointer itself contains the address of the index (remember

 * index[1] == 1).

 *

 * Then to get the trace_array descriptor, by subtracting that index

 * from the ptr, we get to the start of the index itself.

 *

 *   ptr - idx == &index[0]

 *

 * Then a simple container_of() from that pointer gets us to the

 * trace_array descriptor.

 */

static void get_tr_index(void *data, struct trace_array **ptr,

			 unsigned int *pindex)

{

	*pindex = *(unsigned char *)data;



	*ptr = container_of(data - *pindex, struct trace_array,

			    trace_flags_index);

}



static ssize_t

trace_options_core_read(struct file *filp, char __user *ubuf, size_t cnt,

			loff_t *ppos)

{

	long index = (long)filp->private_data;

	void *tr_index = filp->private_data;

	struct trace_array *tr;

	unsigned int index;

	char *buf;



	if (global_trace.trace_flags & (1 << index))

	get_tr_index(tr_index, &tr, &index);



	if (tr->trace_flags & (1 << index))

		buf = "1\n";

	else

		buf = "0\n";
@@ -6205,11 +6242,14 @@ static ssize_t 
trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,

			 loff_t *ppos)

{

	struct trace_array *tr = &global_trace;

	long index = (long)filp->private_data;

	void *tr_index = filp->private_data;

	struct trace_array *tr;

	unsigned int index;

	unsigned long val;

	int ret;



	get_tr_index(tr_index, &tr, &index);



	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);

	if (ret)

		return ret;
@@ -6339,7 +6379,8 @@ create_trace_option_core_file(struct trace_array *tr, 
	if (!t_options)

		return NULL;



	return trace_create_file(option, 0644, t_options, (void *)index,

	return trace_create_file(option, 0644, t_options,

				 (void *)&tr->trace_flags_index[index],

				 &trace_options_core_fops);

}
@@ -6490,6 +6531,15 @@ static void free_trace_buffers(struct trace_array *tr) 
#endif

}



static void init_trace_flags_index(struct trace_array *tr)

{

	int i;



	/* Used by the trace options files */

	for (i = 0; i < TRACE_FLAGS_MAX_SIZE; i++)

		tr->trace_flags_index[i] = i;

}



static int instance_mkdir(const char *name)

{

	struct trace_array *tr;
@@ -6542,6 +6592,7 @@ static int instance_mkdir(const char *name) 
	}



	init_tracer_tracefs(tr, tr->dir);

	init_trace_flags_index(tr);



	list_add(&tr->list, &ftrace_trace_arrays);
@@ -7068,7 +7119,7 @@ __init static int tracer_alloc_buffers(void) 
	 * Make sure we don't accidently add more trace options

	 * than we have bits for.

	 */

	BUILD_BUG_ON(TRACE_ITER_LAST_BIT > 32);

	BUILD_BUG_ON(TRACE_ITER_LAST_BIT > TRACE_FLAGS_MAX_SIZE);



	if (!alloc_cpumask_var(&tracing_buffer_mask, GFP_KERNEL))

		goto out;
@@ -7128,6 +7179,8 @@ __init static int tracer_alloc_buffers(void) 


	ftrace_init_global_array_ops(&global_trace);



	init_trace_flags_index(&global_trace);



	register_tracer(&nop_trace);



	/* All seems OK, enable tracing */

kernel/trace/trace.h

+3 −0
Original line number Diff line number Diff line
@@ -168,6 +168,8 @@ struct trace_buffer { 
	int				cpu;

};



#define TRACE_FLAGS_MAX_SIZE		32



/*

 * The trace array - an array of per-CPU trace arrays. This is the

 * highest level data structure that individual tracers deal with.
@@ -218,6 +220,7 @@ struct trace_array { 
	int			clock_id;

	struct tracer		*current_trace;

	unsigned int		trace_flags;

	unsigned char		trace_flags_index[TRACE_FLAGS_MAX_SIZE];

	unsigned int		flags;

	raw_spinlock_t		start_lock;

	struct dentry		*dir;

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